The consumer market of the multi-sensory detectors such as 3-axis accelerometers, 3-axis magnetometers, 3-axis gyrometers and pressure detector types, is oriented towards always smaller sizes of components to reach a competitive cost.
Thus, the size of a 9-axis detector, including a silicon chip of the microelectromechanical system («MEMS») type, the signal processing electronics comprising the integrated circuit specific to an application (the acronym «ASIC» for «Application-Specific Integrated Circuit») and the package, currently has a dimension of 4×4 mm2 (mm=millimetre) and will very soon reach 3×3 mm2. Such dimensions require the silicon chip alone to have a size of about 4 mm2. In this context of drastic space constraints, the production of MEMS structures comprising 6, 9 or even 10 measuring axes (or measurands) and requiring an important number of pads to provide the interconnection with the reading electronics of each axis, may, in some cases, seem redhibitory. As a matter of fact, this would lead to a size of components larger than the space required for positioning the MEMS structures, and thus entail a much too high cost of production.
Generally, the elements considered as sensitive occupy less than 25% of the total size of the silicon chip. The major part of the surface is dedicated to the tracks routing the signals (supply, detection), to the pads connecting the chip to the external components (ASIC), to the sealing string receiving an additional substrate intended to form a protective cover.
For example, in a 6-axis measuring detector (such as a detector comprising 3-axis accelerometers and 3-axis gyrometers), each of the axes is detected by a Wheatstone bridge. The three Wheatstone bridges required for the accelerometers are connected to distinct supplies; as are the three Wheatstone bridges required for the gyrometers. To eliminate the influence of the parasitic dipoles outside the bridge, the voltage is measured at the terminals of each bridge. Two pads for actuating and controlling the seismic mass are added for each gyrometer, and a self-test pad is added for the accelerometers. Such system requires a minimum of 4 pads for the supply, 12 pads for measuring the voltages supplied to the terminals of each bridge, 12 pads for measuring the unbalance of each bridge, 6 pads for actuating and controlling the seismic masses of the gyrometers and a pad for self-test of the accelerometers. A minimum total number of 35 pads is thus reached, which are often distributed because of the production constraints, on two sides of the chip. For a typical pitch between the pads of 200 micron (μm=micrometer=10−6 meter), one of the dimensions of the chip is 3.6 millimeters minimum. For a minimum dimension in the other direction of about 1.5 to 2 millimeters, a minimum size of the chip ranging from 5.4 to 7.2 mm2 is obtained, whereas the dimension of the currently available products with a detection of the capacitive type is already lower than 5 mm2 and the trend is oriented towards even smaller dimensions. The production of the pads may thus be a limiting factor for reducing the size of the MEMS component.
A need also exists for limiting the electric consumption which is high in the current mountings using Wheatstone bridges.
An object of the present invention is to provide a multisensory detector optimizing the connections and specifically in order to limit the size of the components.
Particularly advantageously, the invention also aims at reducing the energy consumption of such a detector.